1. Field of the Invention
This invention pertains generally to displaying video, and more particularly to communication of tagged video and its up-conversion at the point of display.
2. Description of Related Art
Video communication is widespread throughout our modern society, as video broadcasts are sent over airwaves and over cable TV connections, received by satellite links, communicated over high speed phone lines, and traverse a variety of wired and wireless networks including the internet toward being received by a video driver and output to a display device for viewing by the user. These users expect to view increasingly higher definition video that is sharp and smooth. However, the limits of communication bandwidth to the display device often impairs satisfying these increasing user desires.
Video streams, and in particular high-definition video, requires substantial bandwidth to reach a video display. It will be noted that video is traditionally captured at 24 or 30 frames per second (fps). The legacy standard is 24 fps adopted from film and is strongly entrenched, in particular among cinematographers. Conventional movie projectors advance from one frame of the film media to the next frame 24 times each second. Yet, each frame is illuminated two or three times before the next frame is projected using a shutter in front of its lamp. As a result, the movie projector runs at 24 frames per second, but has a 48 or 72 Hz refresh rate. The higher refresh rate reduces the flickering which would otherwise result if the refresh rate matched the framing rate. Variations from 24 fps capture (“under-cranking” and “over-cranking”) are presently utilized in creation of special effects (e.g. slow motion), while playback is still performed at the 24 fps rate despite the capture rate. While framing rates of 30 fps are legacy standards for video based capture, such as in response to the line frequency of the AC mains which distribute AC power (e.g., 30 fps progressive, 60 fps interlaced, and rates based on 50 Hz power distributions).
Video editing is usually performed using the native (nominal) frame rate of the captured source. Thus, the creative phase of the process typically remains in the native frame rate, to which subsequent rate conversions and compressions are applied as part of the distribution and display process. Techniques such as 3:2 pull-down are used to convert between film and video rates. This may involve duplicating or merging selective frames.
In modern display systems the refresh rate (also referred to as “vertical refresh rate”, or “vertical scan rate” for Cathode Ray Tubes (CRTs)) is the number of times in a second that the display hardware draws the data it is being given. Refreshing is distinct from the measure of frame rate, in that the refresh rate conventionally includes the repeated drawing of identical frames, while frame rate measures only the rate at which the incoming video changes with respect to time.
Refresh rate is an important consideration in modern display devices. For example on smaller computer displays (e.g., CRTs of less than 14 inches) few people notice any discomfort below refresh rates of 60-72 Hz, while on larger CRT monitors (e.g., >17 inches) persons often experience mild discomfort unless refresh rates are set to a more comfortable 85 Hz or higher. Refresh rates often exceed 100 Hz. Non-CRT display technologies each have their own issues in regard to refreshing.
Overall, in order to provide flicker-free output, modern digital displays are moving toward higher and higher refresh rates to improve motion display. It should be appreciated that conventional support of these high refresh rates requires significant bandwidth to the display.
Frame rate converters have been adopted in some display system devices for building intermediate frames based solely on adjacent frames of information in the received video. These converters attempt to glean information from the transmitted video stream which requires substantial video processing capability while often introducing artifacts into the final picture. In particular, frame rate converters suffer the most when the video includes elements such as closed captioning, subtitles, Really-Simple-Syndication (RSS) feeds, picture-in-picture, and so forth that can not be estimated properly from adjacent frames.
Accordingly, a need exists for a system and method of supporting increased refresh rates without a concomitant bandwidth increase to the video display device or the introduction of artifacts.